TIP47: a cargo selection device for mannose 6-phosphate receptor trafficking

Area of Science:

• Cell biology
• Molecular trafficking
• Protein-protein interactions

Background:

• Mannose 6-phosphate receptors (MPRs) mediate the transport of lysosomal hydrolases from the Golgi to lysosomes.
• Efficient recycling of MPRs from endosomes to the Golgi is essential for continuous lysosomal enzyme delivery.

Purpose of the Study:

• To identify proteins involved in the retrograde transport of MPRs from endosomes to the trans-Golgi network (TGN).
• To elucidate the mechanism by which MPRs are sorted and retrieved within the endosomal pathway.

Main Methods:

• Protein binding assays using cytoplasmic domains of MPRs.
• In vitro and in vivo assays to assess MPR transport.
• Identification of specific sorting signals recognized by interacting proteins.

Main Results:

• A 47 kDa protein, TIP47, was identified that selectively binds to MPR cytoplasmic domains.
• TIP47 is required for the in vitro and in vivo transport of MPRs from endosomes to the TGN.
• TIP47 recognizes a phenylalanine/tryptophan motif in the cation-dependent MPR tail, crucial for endosomal sorting.

Conclusions:

• TIP47 plays a critical role in the retrieval of MPRs from endosomes to the Golgi.
• TIP47 acts as an adaptor protein, facilitating the formation of transport vesicles carrying MPRs.
• The interaction between TIP47 and MPRs is key to the proper sorting and recycling of these essential receptors.